Various strategies have emerged in the quest to develop commercially viable, energy advantageous vehicles that use electrical energy in full or in part to propel the vehicle. Of great interest in the context of this invention is the way in which electrical energy is stored, controlled, and replenished in these different strategies.
The increasingly well-known Hybrid Electric Vehicle (HEV) strategy combines a combustion engine with an electric drive system. The electrical energy in the HEV is typically stored in batteries. The battery types or chemistries used to date include lead acid, Nickel Cadmium (NiCd), Nickel Metal Hydride (NiMH), lithium ion, zinc air, and others. Automotive manufacturers including Ford, GM, Mitsubishi, Nissan, and Toyota, to name a few, produce HEVs for the commercial markets. Electrical energy replenishment in the HEV comes from two sources: 1) electrical energy derived from the combustion engine powering an electrical generator, and 2) energy recaptured from regenerative braking wherein the electric drive motors reverse roles under braking conditions and become electrical generators. The first source, combustion engine generation, can operate whether the vehicle is in motion or at rest, but only when the combustion engine is running and consuming fuel. The second source, regenerative braking, only operates when the vehicle is decelerating. Both sources may operate concurrently.
A subtle yet important variation of the HEV is the Plug-in Hybrid Electric Vehicle (PHEV). Otherwise similar to the HEV, the PHEV adds a third source for replenishment of electrical energy in the batteries: 3) electrical grid power connected via an external power cord. Unlike combustion engine generation and regenerative braking, plug-in grid replenishment is only useable when the vehicle is at rest, in the proximity of an electrical outlet, and then only practical when the vehicle is to be parked for some period of time.
The Battery Electric Vehicle (BEV) is similar to the PHEV but lacks the combustion engine component. Batteries and the electric drive are the sole source of propulsion for the BEV. Replenishment is by plug-in only, and as previously stated, only when the vehicle is at rest near an electrical source. Current BEVs are best suited to short and mid range cycles of operation (20 to 200 mile range) requiring recharging periods of several to many hours in between excursions.
A fourth category of sources for battery energy replenishment applicable to HEV, PHEV, or BEV strategies includes all other electrical sources that can be substituted for the grid as a plug-in source. For example, solar power from vehicle born or stationary photovoltaic generators units can and has been demonstrated.
Recent emphasis to improve the practicality of BEVs has been placed upon faster recharging technology. For example, Phoenix Motorcars of Ontario, Calif. and Altair Nanotechnologies, Inc. of Reno, Nev., U.S.A. report a BEV having 35 kWh (kilowatt-hour) battery energy with a 130 plus mile range that can be recharged at a “fast charge station” in as less than 10 minutes. Several hurdles challenge this approach, however. First and most importantly, the energy density, both gravimetric (energy per unit weight) and volumetric (energy per unit volume) is generally inversely related to a batteries maximum electrical current and power handling capabilities. The higher the electrical discharge or charge current the battery can sustain, the lower the energy density tends to be. The fast recharge time comes with the penalty of heavier, larger, batteries and correspondingly reduced vehicle range. Secondly, a 10 minute charge time for a 35 kWh battery implies electrical power requirements in excess of 230 kW, perhaps 40-50 times or more greater than the typical residential electrical service in total, which is why specially equipped “fast charge stations” are specified.
Another electric vehicle strategy is the Fuel Cell Electric Vehicle (FCEV). The FCEV uses hydrogen or other fuel cell technology produce electrical power for the electric motor propulsion system. Although the FCEV strategy typically includes auxiliary electrical energy storage subsystems in the form of either batteries or so-called “ultra-capacitors” for the purpose of capturing regenerative braking energy and other electrical functions, the primary fuel source is typically the fuel in the cells, such as compressed hydrogen, and refueling does not typically involve recharging in the ordinary battery sense.
U.S. Pat. No. 5,187,423 discloses an electrical vehicle energy replenishment system offering uninterrupted operation for electric vehicles by removing batteries from a vehicle and by placing recharged batteries into the vehicle. What is referred to in the '423 patent as “uninterrupted operation” most likely means short interruptions for exchange (versus no interruption). The '423 patent further describes the battery replacement to be accomplished using a semi-automatic lifting device having powerful automatic gripping connectors, the lifting device being capable of handling one or two batteries simultaneously. The '423 patent also discloses a prerequisite condition for the application of the battery interchange system, namely an adequate battery standard providing control over battery attributes including dimensions, voltage, peak current, internal impedance, minimum capacity/weight ratio, and minimum life expectancy.
The '423 patent begins to address the problem of limited operation duty cycle standing in the way of wide spread acceptance of the plug-in recharge electric vehicle variants (motorists often prefer not to have to be “plugged in” for extended periods). However, there are new issues or problems created in the '423 patent disclosure. One issue is the requirements placed upon the replacement (exchange) mechanisms contemplated, those mechanisms being semi-automatic and powerful in nature. It would be preferable if simple, low power, or completely manual replacement or exchanges were possible.
At the other end of this spectrum, as the number of batteries in a given vehicle could be quite large compared to the one or two batteries contemplated in the '423 patent, it is preferable if the entire, large complement of batteries could be exchanged in one cycle by a fully rather than semi automated process. Another issue impeding the system contemplated in the '423 patent is the broad degree of battery standardization envisioned as a preliminary condition to the use of the system. As battery and electric drive technology advances, often in rapid fashion, a system requiring many attributes of the technology to remain fixed will be costly to update and maintain. A better system would require few rather than many aspects of battery and exchange technology to be invariant.
U.S. Pat. No. 5,631,536 discloses an apparatus and methods for the rapid exchange of a discharged or partially discharged battery in return for a charged unit for battery powered vehicles aimed at eliminating the need for a customer to wait during recharging. The '536 patent raises the idea of a vehicle using and its user exchanging multiple batteries but identifies a constraint that the multiple batteries be closely matched in their electrical characteristics to function efficiently together. The '536 patent further proposes a “central database” to track information of all individual batteries to facilitate the matching process when multiple batteries are to be deployed or exchanged. Both concepts, that of a close, intra-group battery matching requirement, and that of a central database are seen as limiting and therefore drawbacks in the context of the present invention.
The present invention contemplates a highly modular, intelligent, quick exchangeable vehicle battery system that addresses many of the shortcomings of preceding BEV strategies. The advantages of the invention will be explained in detail below. However, it is useful as background to examine in survey the parameters of the BEV system. In particular, it is helpful to examine some of the factors involved, including the characteristics of electric drive trains and vehicles, in order to develop an appreciation for the size and nature of the batteries required for a practical vehicle application. The following discussion aims to identify these factors and suggests ballpark values useful throughout the ensuing discussion.
In addition to the battery subsystem, an electrical vehicle propulsion system comprises a power electronics unit, battery charging control circuitry, and an electric traction motor. One commercially available system is offered for sale by AC Propulsion, Inc. of San Dimas, Calif. The AC propulsion system is specified to operate with battery supply voltages of 240 to 450 V. Vehicle power levels of 150 kW (approximately 200 HP) or higher are possible. Continuous operating power in the range of 50 kW (approximately 70 HP) is not unusual. Efficiencies on the order of 85% to 90% are realistic (the amount of battery energy resulting in useful work done propelling the vehicle). Many factors affect the energy efficiency (mileage) of a vehicle including size, weight (number of passengers), aerodynamics, terrain and other conditions, as well as the operating habits of the driver. A small to mid-size exemplary vehicle might achieve average electrical mileage performance in the range of 5 miles per kWh (200 Wh per mile). The same vehicle might achieve satisfactory acceleration and road performance given a peak power level of 85 to 135 HP or about 63 to 100 kW.
The efficiencies and characteristics of the exemplary vehicle described above demand certain characteristics in the batteries. For example, the energy content of the batteries will influence the range of the vehicle in the same way that the liquid fuel content of a combustion engine vehicle determines its range. In both cases, the efficiency of the vehicle drive train comes in to play. In the case of the electric vehicle, we have already mentioned that the efficiency of the propulsion system including the electronics unit, the regenerative charging unit, and the electric traction motor might be in the range of 90%. In addition one must consider the efficiency of the batteries themselves (some energy is lost via power dissipated within the batteries because of internal electrical resistance). This will of course depend on the particular type of batteries being used and the conditions under which the batteries are used. Lithium ion batteries are becoming increasingly attractive for BEV applications because of their high energy density. A lithium-ion rechargeable battery might operate with efficiencies in the range of 95%. The combined efficiency of the propulsion system and the batteries therefore would then be approximately 85%. Thus the net vehicle mileage of 5 miles per kWh at the wheel is reduced to about 4.3 miles per kWh in the batteries. It should be noted that the preceding discussion of efficiencies in the BEV drive train does not include any losses attributable to gearing or mechanical transmission.
The characteristics of a popular lithium-ion battery cell, the ubiquitous 18650 size cylindrical cell, include a nominal diameter of 18 mm and the nominal length of 65 mm of the cell. Variants of this cell are used extensively to power laptop computers. Such cells are readily available in capacities ranging from 1 Ah up to nearly 3 Ah. They deliver most of their energy and charge over a fairly narrow voltage range of 3.5 to 4 V. Peak operating currents ranging from 4 to 10 A or higher depending upon chemistry subspecies may be found. For the sake of this discussion, we will consider a “typical cell”, one delivering 2.2 Ah at 3.6 V and 2.2 A (1C rate). The same cell in new condition would deliver about 8 Wh energy to its load at an 8 W power level over a one-hour interval during a complete discharge from the fully charged state. Peak power capability could be in the range of 16 W or higher. This average cell weighs in at about 45 grams having a cylindrical volume of about 18 cubic centimeters.
From an energy standpoint, the exemplary vehicle described above, getting around 4.3 miles per kWh, would need approximately 4,400 of the typical cells just described to drive a distance of 150 miles. Given a sustained power delivery of just 8 W per cell, these 4,400 cells would provide a sustained vehicle power of about 35 kW (about 48 HP). Peak power for acceleration would be about 70 kW (about 95 Hp). This collection of cells would weigh around 200 kg (435 lb.) and require a space within the vehicle of about 92 liters (3.3 cubic feet). By comparison, the cell count required for a 75 mile range would weigh 100 kg (217 lb.), a 35 mile range 45 kg (100 lbs.), etc.
It should be well noted that the 18650 size cylindrical cell described above is only one of a large number of cell geometries and types contemplated in the present invention for electric vehicle application. Other cell geometries include 26650 and 26700 cylindrical cells manufactured by suppliers such as A123 Systems of Watertown, Mass. and E-One Moli Energy Corp. of Taiwan. These are higher power, lower energy density cells. Compared to the 18650 cell described above, the larger A123 26650 cell delivers 2.3 Ah at 3.3 V and up to 70 A (30C rate) continuously or 120 A peak, delivering perhaps 6 Wh energy to its load at 100 W power levels. It weighs approximately 70 grams and has a cylindrical volume of about 34.5 cubic centimeters. The E-One Moli Energy 26700 cell delivers 2.9 Ah at 3.8 V and up to 15 A (5C rate) continuously, delivering perhaps 11 Wh energy to its load at 50 W power levels. It weighs approximately 100 grams and has a cylindrical volume of about 37 cubic centimeters.
The foregoing analysis shows that a collection of batteries large enough to have sufficient energy for reasonable driving ranges (35 miles or greater) weigh more than most humans would be comfortable handling. Generally vehicle weight is a significant variable determining vehicle mileage (energy efficiency), heavier vehicles getting lower mileage than lighter ones. One can also see that a weighty cache of batteries, while needed for extended range driving, equates to excess weight in shorter excursions detracting unnecessarily from vehicle operating efficiency. When short excursions are planned, it would be advantageous to adjust the amount of batteries on board so that the vehicle weight would be lessened and its efficiency improved.
As batteries age and go through an increasing number of charge and discharge cycles they wear out. This wear manifests itself in a decrease in battery capacity. The rate at which capacity is lost over time and use depends in complex ways on the chemistry of the battery, temperature, rate of charge, rate of discharge, depth of discharge and state of charge, time, and other factors. From the standpoint of the electric vehicle application, the “age” of the batteries will determine a reduction in the maximum range of the vehicle. Put another way, at any point in time, the maximum driving range of a vehicle with fully charged batteries will be a function of not only the number of batteries but also the cycle age of the batteries. In short, older batteries are depreciated and valued less than newer batteries with higher capacities.
Previous BEV applications operate under the tacit assumption that the batteries “built in” to the vehicle would discharge, charge, and age together as a synchronized group. Although the maximum operating range of such vehicle decreases over time and is expected, the previous BEV system provides no mechanisms to allow disparately aged or charged batteries to be efficiently utilized. Such mechanisms are provided by the present invention.
U.S. Pat. No. 6,465,986 B1 issued Oct. 15, 2002 discloses battery interconnection networks electrically connected to one another to provide a three-dimensional network of batteries. Each of the interconnection networks comprises a battery interconnection network having a plurality of individual component batteries configured with compound series parallel connections. A plurality of rows of individual component batteries are connected in parallel. A plurality of columns of individual component batteries are interconnected with the plurality of rows with each column having a plurality of individual component batteries connected in series with an adjacent individual component battery in the same column and electrically connected in parallel with an adjacent individual component battery in the same row.
McDowell Research Corporation of Waco, Tex. produces a Briefcase Power System for powering transceivers with an advertised DC input range of 11 to 36 VDC and an AC input range of 95 to 270VAC at 47 to 440 Hz. No outputs are specified in the advertisement at www.mcdowellresearch.com.
Automated Business Power, Inc. of Gaithersburg, Md. produces an Uninterruptible Power Supply Transceiver Power Unit with advertised DC input range of 9 to 36 VDC and AC input range of 85 to 270VAC at 47 to 440 Hz. Two outputs are specified both at 26.5VDC, one at 5.25 A and one called auxiliary at 1 A. Battery chemistry is not specified in the advertisement at www.abpco.com, but indications are given that non-compatible battery types including primary Lithium battery (BA-5590/U), NiCd (BB-590/U), NiMH (BB-390A/U) or any other non-compatible type shall not be useable.
There is a need for a lightweight intelligent energy system for use in a variety of applications including for use in energy supply systems for homeland defense, military, industrial and residential use. There is also a need for light-weight energy systems including battery systems for use in vehicles, cars, trucks, military vehicles and the like which can be refueled by swapping individual batteries or groups of batteries at energy filling stations much like the typical gas stations.